The dissertation is devoted to the development of a starter preparation made on the basis of lactic acid bacteria (LAC) isolated from natural econishes and intended for the production of cheese.
At the initial stage of development of the starter preparation, were studied the probiotic and technological properties of E. durans SB6, E. faecium SB12, E. durans SB18 and E. durans SB20 isolated from traditional Carpathian cheese.
It was established that the studied strains of enterococci showed different antagonistic activity to opportunistic microflora, in particular, E. coli, S. enteritidis, E. aerogenes, P. mirabilis, P. aeruginosa, but to the gram-positive microorganisms (S. aureus) antagonistic activity have not been established. As the temperature of cultivation of enterococci increased (20, 30 and 37°C), their antagonistic activity also increased. In particular, the most optimal cultivation temperature was 37°C. Under these conditions, the E. durans SB18 strain showed the most pronounced antagonistic activity against all tested gram-negative microorganisms, including P. aeruginosa.
The studied strains were sensitive to a wide range of antimicrobial drugs, with the exception of gentamicin, streptomycin, kanamycin and penicillins. Importantly that all strains of enterococci were susceptible to vancomycin. Under conditions of simultaneous cultivation of enterococci with opportunistic microorganisms were found different effects on increasing their sensitivity to antibiotics. For example, strains of E. faecium SB12 and E. durans SB18 increased the sensitivity of S. aureus to gentamicin by 16,2 and 14,8%, respectively, and the co-cultivation of S. aureus with enterococcus did not affect the change in sensitivity to amoxicillin. At the same time, the E. durans SB18 strain showed a more pronounced effect on the change in sensitivity. The E. durans SB18 strain contributed to increasing the sensitivity of S. aureus to vancomycin.
Strains of enterococci isolated from traditional Carpathian cheese in different quantities synthesized biologically active substances. It was established that the E. durans SB18 strain synthesizes the largest amount of amino acids, in particular, essential amino acids – lysine, trethionine and leucine + isoleucine, the concentration of which was higher, respectively, by 10,3, 39,5 (p<0.05) and 5,8%, and also non-essential amino acids serine and glycine, the concentration of which was, respectively, 30,0 and 16,2% (p<0.01) higher compared to the control. Enterococci synthesized vitamins of group B, among which vitamin B1 the most. The concentration of vitamin B1 increased from 8,5 to 10 times (p<0.001), vitamins B3 and B5 are also synthesized in significant quantities.
It was found that all studied strains produced small amounts of acetic and propionic acids, but only the E. durans SB18 strain was capable to synthesize lactic acid, in particular, it's concentration probably increased by 2,6 times (р<0.01) compared to the control.
Toxico-biological studies have established that the studied strains of enterococci are not pathogenic, not infectious, do not have catalase activity, do not produce lecithinase, plasma coagulase, and fibrinolysin, which makes it possible to classify these microorganisms as harmless to the macroorganism.
The studied strains showed high technological properties, in particular, E.durans SB20 and SB18 strains showed the best acid-forming properties, as they were able to reduce the pH of the medium during their cultivation as on 24 h and 48 h under different temperature regimes, herewith the pH value reached 5 units and less. In addition, the investigated enterococci accumulated biomass in different ways, and also there were noted interspecies and interstrain differences. The highest growth intensity by the cultivation temperature of 37°C was observed in the cultivation of strains E. durans SB18 and SB6. Enterococci strains showed high salt resistance.
Enterococci tolerated the adverse conditions of the digestive tract well, in particular, they survived and multiplied in conditions of different pH values of the environment and different concentration of bile. It was established that out of the four studied strains of enterococci at pH 4, two strains E. durans SB18 and E. durans SB20 survived and showed good growth properties. When E. durans SB18 and E. durans SB20 strains were cultivated at pH 5, the optical density of the medium was in 9.8 and 10.8 times higher, respectively (p<0.001). The same strains showed the best growth properties at pH 6 and 7 units. When the studied enterococci strains were cultivated in a medium with 20 and 40% bile and high concentrations of sodium chloride from 3 to 6.5%, they maintained their viability for 21 days.
